Task-based Coordination of Flexible Manufacturing Cells using Petri Nets and ISA standards

This work presents an approach to describe the event-based coordination of standard Flexible Manufacturing Cells using Petri Nets and its translation to local controllers with computer-based supervision. The plant model is constructed by the interconnection of individual Petri Net models describing the relationships of equipment and storages with process tasks and their logical precedence restrictions, according to the suggestions of the ISA-95 standard. The modeling is generic and scalable containing the possible restrictions about concurrent production routes, equipment availability, storage limitations, sharing resources, etc. A procedure about the codification of the Petri Net model into a software application is presented. The result is a hierarchical setup, where the process tasks can be programmed in local controllers, like PLC's networks. These tasks are communicated and coordinated by a software application using the Petri Net model. A sequence of tasks is obtained by the firing of transitions of the Petri Net model and the system becomes flexible producing different and concurrent products. The approach is tested in a prototype of automated manufacturing cell using a PLC and the development of a software application in Matlab®, which can be extended to other industrial manufacturing cells.